The term “photonic” has been coined in the art of optical communications by analogy to the term “electronic.” A “photonic” device is one which processes an optical frequency communications signal. Although the signal processing elements in a photonic device are optical in nature, and many do not require any form of electronic signal processing, most photonic devices in common use incorporate various types of electrical or electronic connections, whether it be a heater, a photo detector, or other electrical or electronic devices.
The electrical contacts employed in photonic devices are subject to corrosion when exposed in use to moisture and oxygen, greatly reducing the lifetime of such devices. There is considerable premium associated with the exclusion of moisture and oxygen from photonic packages. This is particularly problematical because many such devices need to be coupled to fiber optic inputs and outputs. In a typical application in the art, an optical fiber array is sealed into a ferrule that is then inserted into a receptacle in the housing of the photonic device package; the connection so formed then being sealed to provide a hermetic seal. It is important in this application that the permeability of the ferrule material itself be of low permeability to oxygen and moisture. Typical photonic device packages are welded or soldered metal boxes, although they may be low permeability plastic.
In common practice is the use of an all metallic sealing means. For example, metal-coated optical fibers are soldered to a metallic ferrule, which is in turn inserted into a receptacle mounted upon, or integral to the housing of the photonic device, and the connection is then soldered to provide a hermetic seal.
See, for example, Filias; Materials Research Society Symp. Proc. Vol. 531, 1998, p. 263-272.
It is further known to prepare ferrules from injection molded polymers having ceramic inserts, as described in U.S. Pat. No. 5,568,581. However, there remains a need for inexpensive directly moldable plastic ferrules which offer high processibility combined with excellent barrier properties and low coefficient of thermal expansion (CTE).
One such material, which has been suggested in the art, is a liquid crystal polymer (LCP). LCPs are known to offer excellent molding performance, very high barrier to moisture and oxygen, low CTE and good thermal performance.
Farrell et al., “The Liquid Crystal Packaging Solution,” Proceedings of the 2003 International Symposium on Microelectronics, pp. 18-23, discloses the use of metal plated LCP lids suitable for solder sealing to an LCP printed circuit board having molded-in wire interconnects. Also disclosed therein is an example of two optical fibers passing through the sidewall of an LCP package.
Metallization of LCP is known. Beitinger et al., WO99/39021, disclose sputter coating, ion-plating, and electroplating of LCP to achieve a metallized surface thereof.